The spacers between cogs on most freewheels are plastic, if you use the torch you'll melt them for sure. The cogs are also likely hardened. If anything, you might try "freezing" the body with CO2 or an air duster, but I wouldn't use anything harsher than a blow-dryer for heating. Even if you have new spacers, the burnt-on grease and plastic will be a real beast to clean off.

Have you considered just rebuilding the freewheel? If the cogs aren't worn then the bearing surfaces likely aren't either, mostly they just get really dirty. Of course that's only an option if your smallest cog is big enough for you to disassemble the body without removing it.